The present invention relates to a novel process for the use of an X-ray tomo-scanner which, by certain adaptations, makes it possible to use it for carrying out cinedensigraphy, whilst sill maintaining a normal operating mode. It also relates to a tomo-scanner suitable for use in cinedensigraphy in this way.
Cinedensigraphy techniques have been known for a long time and were developed in France by Mr Henri-Maurice MARCHAL and are described for example in Volume 1 of the work entitled "Traite de radiodiagnostic" by J. BUTREIX, V. BISMUTH and M. LAVAL-JEANTET, published by Masson et Cie, pp.372ff.
The hitherto known method for obtaining a cinedensigraphic recording comprised irradiating the area of the patient to be observed by an X-ray beam, collecting the transmitted X-rays on a detection cell, converting them into an electrical signal and recording the amplitude of said signal as a function of time.
This method was mainly used for defining and locating abnormalities in the lungs. Thus, an abnormality such as a tumour modifies the movements in the lung in its breathing function and affects the vascular system. If it is possible to observe the amplitude of the movements in the different areas of the lungs it is possible to define the areas in which these movements are abnormally small and correspond to an abnormality. It is also of interest to be able to observe how, over a period of time, the density of the different zones observed behave, even if there are no deformations of organs.
In this hitherto known method the collected electrical signal, which varies in time, corresponds to an integration of the information over the entire area considered by the detection cell. This integration takes place not only on the thickness of the subject traversed by the X-ray beam, but also on the surface of the subject corresponding to the cross-section of the irradiating beam.
The fact that it is necessary to have specialised equipment has meant that this cinedensigraphy method has stayed at the laboratory stage, in spite of the interesting results which it can provide on the behaviour over a period of time of organs exposed to X-rays.
In addition, tomo-scanning or transverse axial tomography techniques are known. Unlike cinedensigraphy which attempts to obtain information on attenuation variations over a small area as a function of time, tomo-scanning makes it possible to reconstitute the linear attenuation coefficient value at any point of a section or cross-section and reconstruct the image of this section. However, it only gives good results if the object examined is strictly identical to itself at all times during scanning. Unless this complete absence of variation in time of the shape and/or density of the examined object is ensured, the reconstituted image is imprecise or blurred.